So you're actively planning on adding power creep? 
Well, it's your game I suppose.

Anyway, if Zeta is the limit, doesn't that bring Haros and the Learning Computer from original Mobile Suit Gundam (though the Haro also appeared in Zeta) into play? I mean, we could just say mine has a last-gen, more robotic type, the gmpc you're bringing in has a next-gen, more human type? That way yours is still special and impressive and I get to do my thing in the corner. Sound okay to you?
Furthermore you mention combiners aren't in play, but the Core Block System and G-Parts/G-Fighter of the original RX-78 Gundam were pretty much the same concept. I mean, assuming when you say "combiner" you're referring to a mecha formed from component machines like Getter Robo or Combattler V, rather than something like ChoRyuJin or Big Rayearth.